Internal combustion engines typically require liquid fuel to operate. Typically the fuel is contained in a fuel tank adjacent to the engine. The fuel tank is sized to permit the internal combustion engine to operate for a predetermined amount of time. However, once the liquid fuel in the fuel tank is used up, it becomes necessary to replenish the fuel in the fuel tank. Typically a filling tube is provided for this purpose with a mouth sized and shaped to receiving a refueling nozzle from a gas pump, for example, of the type found at conventional filling stations. When the filling tube is not being used, a fuel cap or gas cap is used to close the mouth of the filling tube to prevent evaporation and spilling of the fuel. Although many types of gas caps have been made in the past modern gas caps are typically provided with external threads, which mate with internal threads formed on the inside of the mouth of the filling tube, whereby the gas cap can be screwed into place. Most modern gas caps are also provided with a slip mechanism, which prevents the gas cap from being over-tightened in the filler tube.
In the past gas caps and filler tubes were typically made from metal, with the exception of a compressible elastomeric gasket that was used to ensure a vapour tight seal around the mouth of the filler tube. However, over time, as plastics have become of better quality and higher strength, noncorroding plastic has replaced many of the corrodible metal elements of the filler tube and gas cap, until gas caps are now made almost entirely out of plastic. Plastic has certain advantages as a gas cap including being completely resistant to corrosion and being somewhat less expensive.
Although mostly made from plastic, certain metal elements remain in use in gas caps. Specifically, the gas cap can be made with a plastic handle portion with a depending skirt or lip and a plastic plug portion on which the threads are formed. However, to provide enough strength it has been necessary to use metal components in the gas cap assembly as structural elements. The plastic was simply not strong enough, given the designs of gas caps, to be used. However, using metal in combination with the plastic is not the best solution as the metal components will still tend to corrode and weaken over time and can lead to premature failure of the gas cap, even though the remaining plastic components are not corroded. Further metal is more expensive than plastic.
What is desired is some method and apparatus for replacing the metal structural elements with plastic elements. What is desired is a design for a gas cap which permits a noncorroding material such as plastic, to be used, without compromising the structural strength of the gas cap.